With the development of information technology and networks such as Internet and intranets, more and more information exists online. The vast amount of online information may overwhelm a user who wants to find something that might be of interest to him. Hence, more attention has been paid to filtering out unnecessary information and receiving only the information needed. One method useful for such purposes is providing a summary of a document or summarizing a document so that the user may be allowed to preview the summary and decide whether it would be worthwhile to acquire and read the full document.